Such a device, an air cannon, is among other things described in U.S. Pat. No. 3,788,527, wherein a pressure tank via an outflow opening, which is locked by means of a piston, can at a given moment be suddenly emptied via a tube. This piston is placed in a cylinder and can be brought into two possible end-positions. In the one end-position the outlet opening of the pressure tank is closed, in the other end-position open. The piston and the cylinder must, within a certain tolerance, be quite exact in diameter.
The aim of the invention is an air cannon, whereby parts can be used, which need not be manufactured with great precision, so that an apparatus can be constructed that will be cheaper than the known air cannons. Another aim of the invention is an air cannon, which can release the air faster than the up till now known air cannons.
This object of the invention is achieved with an air cannon according to the invention, wherein that on the bottom of the second tube more or less concentric to the aforementioned tubes, a third tube with a smaller diameter and shorter than the second tube is airtightly fastened on it with the one end being of such a length that between the ends of the first tube and the third tube, there is a space left inside the second tube, wherein a disk is placed, which near the circumference is provided with two collars, which project to both sides and stand some-what slanting outward, so that the disk can be moved back and forth between the ends of the first and the second tubes. With such an apparatus it is possible to open the pressure tank very quickly because the piston can be made very light. Also normal tubes can be used without the walls needing an extra machining. An extra advantage is that if the piston is moved in the open position, then an amount of air under pressure will be enclosed between the second and the third tube and the disk, so the disk is slowed down before being pressed onto its seats. The application of a disk to block the outlet opening of the pressure tank is already known from the European patent application published under number 0 021 999 but in that construction the disk is moved back and forth between the two possible extreme positions by means of a resilient membrane. That construction has the disadvantage that a membrane within a certain time period will show breakage, because rather high demands have to be made of the membrane.
In a preferred embodiment of the air cannon according to the invention, the second tube is fastened on a flange, which forms the bottom of this tube and which flange can be airtightly fastened to a flange of the pressure vessel. This construction makes it easy to replace the mechanism for the blocking of the outlet opening of the pressure tank, if this shows defects.
Preferably, the inlet opening, through which the pressure tank is filled with air, is made in the flange; naturally, it is also possible to bring on this opening directly in the wall of the pressure tank or as is generally done at present in the wall of the second tube, whereby this opening has been placed such that, at the moment that the piston blocks the outlet opening, the openings via the in and outlet opening in the bottom of the third tube let through the air to the pressure vessel, while if the outlet opening is opened and the disk is placed in the other end position, then the openings in the wall of the second tubular part do not stand in communication with the in and outlet opening in the bottom of the second tube.
The disk is preferably made out of a metal disk covered by rubber or plastic sheet; the collars are also made of rubber or plastic whereby these are somewhat resilient.